The present invention relates generally to engines and, in particular, to systems and methods for determining an optimal substitution rate of fuels, and controlling the fuels being injected to a plurality of cylinders of such engines.
Generally, engines such as dual-fuel engines are alternative internal combustion engines designed to run on more than one fuel each stored in separate vessels. The dual-fuel engines are known for various applications, such as generator sets, engine-driven compressors, engine driven pumps, mechanical machines, off-highway trucks and others. Such dual-fuel engines are capable of burning varying proportions of the resulting blend of fuels in the combustion chamber and the fuel injection and/or spark timing may be adjusted according to the blend of fuels in the combustion chamber.
The dual-fuel engines operating with a high fraction of non-premixed, direct injected fuel, such as diesel fuel, and with a less fraction of premixed fuel, such as natural gas may have uneven exhaust residuals between cylinders due to flow dynamics which may limit natural gas substitution in one or more cylinders. Such exhausts residuals may include pollutants such as carbon oxides (e.g., carbon monoxide), nitrogen oxides (NOx), sulfur oxides (SOx), and particulate matter (PM), which may be detrimental to the environment. The amount and relative proportion of these pollutants may vary according to the fuel-air mixture, compression ratio, injection timing, environmental conditions (e.g., atmospheric pressure, temperature, etc.), and so forth. Similarly, the dual-fuel engines operating with the high fraction of premixed fuel and with the less fraction of non-premixed fuel may be susceptible to knocking in each cylinder and may have peak cylinder pressure issue. Therefore, determination of an optimal substitution rate of certain amount of the heavy fuel with the lighter fuel using one or more known techniques may be difficult and unpredictable.
Thus, there is a desire for an improved system and method for engines operating on more than one fuel.